Single-atom coordination-dependent catalysis for peroxymonosulfate-mediated water purification

Single-atom catalysts (SACs) have been extensively employed for peroxymonosulfate-based advanced oxidation processes (PMS-AOPs), because of the maximum atomic efficiency offered by homogeneous-dispersed metal atoms and facile recyclability attained by the heterogeneous substrate. Intriguingly, though SACs with atomically isolated metal–nitrogen moieties have shown exceptional activities in PMS-AOP-based water treatment, their catalytic performances and mechanisms varied with the structures. In this review, the catalytic mechanisms of SACs/PMS systems were summarized. Specifically, nonradical reactive oxygen species are involved in the majority of the reactions, while singlet oxygenation, electron-transfer, and high-valent metal-oxo species are identified as dominant nonradical pathways. We also discussed the effects of metal center, metal loading, and substrate on the overall catalytic activities and mechanisms in PMS-AOPs. The pivotal roles of coordination environment in modulating the activity of SACs and reaction pathways were highlighted. Furthermore, an outlook on future challenges and prospective for SACs in water purification is presented.